Adjustable throttle with flat channel cross-section

ABSTRACT

The invention relates to an adjustable throttle with which to influence the mass flow within a rectangular flow channel or a flat flow channel with rounded marginal areas. Because of its special design, the throttle has no parting plane perpendicular to the fluid flow direction. The channel height may be modified by this throttle, so that the fluid mass flow may be influenced by changing the local flow channel resistance as a function of its width without creating discontinuities in the flow channel. Because of this continuous change in the geometry of the flow channel, both in the direction of its width and in the flow direction, the whole flow channel is totally free from dead spots.

The invention relates to an adjustable throttle having a flat flowchannel with a width to height ratio or a circumference to height ratio,respectively, of at least 10 for the guidance of a mass flow of freeflowing material, comprising an inlet portion and an outlet portion anda central flow channel portion interconnecting these two channelportions, the flow channel being free from parting planes and free fromdead spots throughout the flow channel portion between the flow channelinlet and the flow channel outlet, and its channel height beingmodifiable, in the central flow channel portion, from the outside by wayof adjusting means by elastic deformation of the wall of at least onewall portion by more than 0.1 mm.

BACKGROUND ART

An adjustable throttle of the generic type mentioned above is known fromU.S. Pat. No. 3,884,611. In this throttle, the flow channel is plane. Arecess is formed in a thick-walled limiting wall of the flow channel insuch a way that a thin wall portion is formed. This wall portion, whichis equally flat, i.e. plane, in its position of rest, can be deformed ina direction right into the flow channel by screws as adjusting means,i.e. it can be curved slightly, which renders possible an adjustment ofthe channel height. On the one hand, the possibilities of making aninfluence on the channel height are limited, since the thin wall portionis elongated, which is possible only to a limited extent. Moreover,after numerous adjusting operations, the material of this thin wallportion will deform plastically, no longer returning elastically intoits initial position.

U.S. Pat. No. 3,122,789 teaches an extrusion die which has a straightflow channel. A wall of this flow channel can be deformed by hydraulicpressure for the width of the opening of the slit die to be changed atits outlet portion. Apart from the fact that throttling does not takeplace in a central flow channel portion between an inlet portion and anoutlet portion, the adjusting problems are the same as mentioned above.

OBJECT AND SOLUTION

It is the object of the invention to develop a metal throttle that isadjustable with great sensitivity and by means of which, over the widthof the flow channel, a mass flow that passes through can be modified.Further, it is the object of the invention to produce coextruded sheetsof a constancy of layer thickness not achievable so far by the use ofthe apparatus according to the invention.

According to the invention, this object is solved in that the flowchannel has a curvature and in that the elastically deformable walldefines the flow channel in the vicinity of the latter's curvature.

Further, it is advantageous if flow channel portions of non modifiablegeometry are located before and behind the flow channel portion.

In keeping with another advantageous embodiment, the adjusting range ofthe adjusting member is at least 0.1 mm.

According to another advantageous embodiment, provision is made, in thevicinity of the adjusting members, for the flow channel to have portionsof a channel height H, to which applies: H<5 mm.

It is especially advantageous if the wall, where elastically deformable,has a wall thickness A, to which applies: A<6 mm and preferably 0.5mm<A<4 mm.

In keeping with yet another advantageous embodiment, the distance of theadjusting members from each other is less than 15 mm.

It is further of advantage if the flow channel is treatable and locatedin an extrusion die.

According to another advantageous embodiment, the flow channel islocated in a coextrusion adapter.

Finally, it is of advantage if the elastically deformable wall definesthe flow channel on the latter's outside in the vicinity of the latter'scurvature.

The object of the invention is attained by a construction as seendiagrammatically in FIG. 1. The width to height ratio of the flowchannel should exceed 10, however preferably amount to 20 to 5000. Theadjusting range of the adjusting members 5 should be at least 0.1 mm,preferably 1-1.5 mm, for sufficient modification of the flow channelresistance over the width of the channel to be achieved locally. Inorder to ensure this adjusting range, the wall 4 should have at least aslight curvature and a wall thickness A of <6 mm, preferably of 0.5 to 4mm. An adjustment working at a narrow distance over the flow channelwidth is achieved by the flexibility thus produced of the wall and by assmall as possible an adjusting screw distance of <40 mm, preferably of<15 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an elevation sectional view of the throttle according tothe invention.

FIG. 2 shows the throttle according to the invention incorporated intoan extrusion die for flat plastic sheets.

FIGS. 3 and 4 show the throttle according to the invention incorporatedinto a multichannel die.

FIG. 5 shows the throttle according to the invention incorporated in acoextrusion adapter.

ADVANTAGE OF THE INVENTION

Conditioned by the minor thickness A seen in FIG. 1 of the wall 4 of theflow channel portion 3, the wall exhibits high flexibility so that, dueto the low deformation forces required, it can be deflected locallydefined in the direction of the flow channel 3 with the aid of adjustingscrews 5 of small dimensions. The height H of the flow channel 3 throughwhich flow takes place can be modified with great sensitivity, whichresults in the mass flow being effectively influenced.

The throttle only consists of 3 parts, the upper half 6, the lower half7 and the central piece 8. As a result, it has no parting planeperpendicular to the flow direction in the vicinity of the flow channel.There are only the two parting planes between the three pieces 6, 7 and8. They extend in the direction of the flow channel in the two marginalareas of the flow channel, there being almost no risk of materialstagnation. Additionally, the risk of leakage is very low. The specialconstruction ensures that the geometry of the flow channel can changeonly continuously in the flow direction. Consequently, no dead spots canoriginate due to discontinuities in the flow channel height as isinevitably the case with the baffle beams projecting into the flowchannel.

The adjustable throttle described serves to change the total mass flowalthough the driving pressure difference is constant. This is realizedby adjusting all the adjusting members by the same amount. The mass flowdistribution over the width of the flow channel can be modified, too.This is realized by adjusting individual adjusting members. Thisspecific throttle construction is especially suitable for influencingthermoplastically workable masses, preferably plastics of all types suchas PE; PP; PS; PVC; PMMA; PC; PA; PSU; PES; and PEEK. It is alsopossible to influence non polymeric masses as long as they exhibitsufficiently free flowing properties.

EMBODIMENTS OF THE INVENTION

A throttle of this design can be incorporated in any structural membersthat have a fluid flowing in a flat flow channel inside of them. Theintegration into tools as used in plastics processing is of specialinterest. FIG. 2 illustrates the use in an extrusion die for theproduction of flat plastic sheets. The melt flows through a narrow meltchannel 10 into the die and is distributed in the distribution channel11 to have the die outlet width. The flexible wall 4, which can bechanged locally in spatial position by adjusting means 14, extends overthe entire width of the adjoining flow channel portion 12.

This throttle portion is again followed by a channel portion 15 of nonmodifiable flow channel geometry. The wall 4 has a 90° curvature, whichis of advantage in two aspects. Firstly, the flexibility of the wallincreases, and secondly, this serves to deflect into the perpendicularthe melt flowing from the, as a rule, horizontal extruder into the die.For past experience has shown that the vertical supply of melt into ahorizontal smoothing unit is more advantageous than the horizontalsupply into a vertical smoothing unit. In this case, the flexible wallis part of a separate central die piece 16, which is screwed to the diehalf 17 in the vicinity of the inlet channel 10 and soldered or weldedto the die half 17 in the vicinity of the channel 15.

In similar fashion, the throttle may also be incorporated in amultichannel die. Such a solution is seen in FIGS. 3 and 4. Inparticular in the field of multichannel dies, there is still a deep gapbetween the requirements of the processing industry and thetechnological possibilities presently available and known. Byintegrating the throttle according to the invention in the secondarychannel 40, it is possible, over the width, to take influence on themelt flow of the secondary layer before the channel portion 43 in such away that, in the channel portion 41, a melt flow that is almost constantover the entire channel width can be placed on the main layer melt thatflows through the flow channel 42.

For the first time, the throttle integrated in this way into thesecondary channel of a multichannel die offers the constructionalprerequisites for thickness control of individual layer over the widthof the sheet. The constructions of baffle beam adjustment known so farhave not been suitable for layer thickness control because of the highadjusting forces needed. Only the flexible lip, which demands only forlow adjusting forces and in which the elastic forces of steel and theinternal pressure by the fluid provide for restoring force to beavailable, renders possible a mass flow control of individual layersover the width of the flow channel in dependence on the layer thicknessmeasured at the product.

As shown in FIG. 4, the throttle according to the invention for thefirst time offers the possibility of controlling the thickness of asecondary layer by means of a control unit in a multichannel die. Twomelt flows are produced by the extruders 27 and 28 and fed into themultichannel die 30. By measuring the thickness of the secondary layerafter it has left the tool 26 by means of a selective film thicknessmeasuring device 34 and by comparison of the nominal and actual valuesin a control unit 35, the adjusting means 36 can be triggeredspecifically, differences in film thickness thus being balanced over thewidth of the sheet. Nowadays, selective methods of film thicknessmeasuring on a line are available and control algorithms suitable forthis job are background art in the field of sheet production. The sheetcan be smoothed by means of smoothing rollers 33 and cooled. In the caseof a profile, cooling may take place by way of a stationary calibrationequipment through which the profile is passed.

FIG. 5 illustrates the use of the throttle in a coextrusion adapter. Inthis case, too, a flow channel portion 20 of non modifiably geometry islocated before the actual throttle in the flow channel for thecoextrusion melt and another flow channel portion 22 of non modifiablegeometry is located at the end, after the coextrusion channel has openedinto the flow channel 21 for the main melt. The throttle is formed bythe thin wall 4, which can be changed in position by way of adjustingmeans 24.

In all the types of use, the flow channel resistance can be modifiedover the width with great sensitivity by actuation of the adjustingmembers. Undesired differences in melt flow can be balanced over thewidth of the flow channel. Even a desired melt flow profile can bespecifically produced over the width of the flow channel, as isfrequently necessary with coextrusion adapters.

Adjustable throttles that are free from dead spots can also be used byadvantage for controlling the mass flow ratio in divided flow channels,which are fed for instance by a single extruder. This is often the casewith profile dies, where a precise wall thickness relation is to beachieved between different walls that are fed from a single mainchannel. For instance, it can be highly interesting in the case ofribbed twin slabs to be able to modify, in certain portions, therelation of rib thickness to chord thickness in spite of given flowgeometries in the die. If, as in the case of ribbed twin slabs of PC,the chords are coextruded, having a weather resistant film, then it isof great importance to keep a precise pressure ratio in the rib andchord flow channels in order to avoid interfering thickenings ortaperings of the coextrusion film in the inlet portion of the ribs. Byintegrating an adjustable throttle according to the invention into oneof the two flow channels, the flow channel resistance relative to theother flow channel can be changed. The results are modified mass flowconditions and modified marches of presssure in the flow channels.

I claim:
 1. An adjustable throttle for guidance of a mass flow offree-flowing material, comprising:a flat flow channel having a width anda height and a width to height ratio of at least 10; an inlet portion(1) of said flat flow channel; an outlet portion (2) of said flat flowchannel; a central flow channel portion (3) interconnecting said inletportion (1) and said outlet portion (2); an elastically deformable wall(4) defining said central flow channel portion (3); and adjusting meansdirected from outside towards said elastically deformable wall (4),wherein said flow channel is free from parting planes perpendicular to aflow direction and free from dead spots throughout said central flowchannel portion (3), wherein said central flow channel (3) has a curvedbend, wherein said elastically deformable wall (4) defines the flowchannel in the vicinity of said curvature, and wherein said height ofsaid flat flow channel is adjustable by more than 0.1 mm by means ofsaid adjusting means.
 2. A throttle according to claim 1, wherein flowchannel portions of non-modifiable geometry are located upstream anddownstream of said central flow channel portion (3).
 3. A throttleaccording to claim 1, wherein said adjusting members have an adjustingrange of at least 0.1 mm.
 4. A throttle according to claim 1, wherein inthe vicinity of said adjusting members, said flat flow channel hasportions of a channel height H, to which applies: H<5 mm.
 5. A throttleaccording to claim 1, wherein said elastically deformable wall (4) has awall thickness A, to which applies: A<6 mm.
 6. A throttle according toclaim 1, wherein said adjusting members have a distance from each otherwhich is less than 15 mm.
 7. A throttle according to claim 1, whereinsaid flat flow channel is treatable and located in an extrusion die. 8.A throttle according to claim 1, wherein said flow channel is located ina coextrusion adapter.
 9. A throttle according to claim 1, wherein saidelastically deformable wall (4) defines the flow channel on an outsideof said curved bend.
 10. A throttle according to claim 5, wherein saidelastically deformable wall (4) has a wall thickness A, to whichapplies: 0.5 mm≦A≦4 mm.